Digital wireless data transmission is used in a wide variety of systems that present a great variability in data rate, transmission range, and power consumption.
Are also known in the art communication systems using digitally synthesized chirp symbols as modulation, and suitable FFT based receivers. European patent application EP2763321 describes, among others, one such modulation method in which the phase of the signal is essentially contiguous, and the chirps are embedded in data frames in in such a way as to allow synchronization between the transmitter and receiver nodes, as well as determining the propagation range between them. This modulation scheme is used in the long-range LoRa™ RF technology of Semtech Corporation, and will be referred simply as ‘LoRa’ in the following of this document.
There is a need in the art for a digital transmission scheme that partners a long transmission range with low power consumption, and can be realized with simple receivers and transmitters.
Most wireless networks implement a control, from the network, of the endpoints. For instance, in 2G/3G/4G cellular networks, the endpoints need to get their access granted before using the network, and the network controls their transmission speed and transmission power. The control is performed using the same packets as for data, possibly the control is piggybacked in data packets. This allows a reliable transmission of the control information. WiFi networks have a much simpler medium access control. The endpoints implement a “listen before talk” mechanism. In addition, link rate adaptation is performed in an implicit manner: from transmission error statistics of packets with various data rates, the best rate is chosen for most of the packets exchanged. Reliable transmission of the information is achieved thanks to acknowledgement packets. These techniques assume a significant amount of downlink transmission because the networks are either symmetrical for voice operation, or downlink dominated for data access. Further, these techniques increase the required listening time of endpoints. Therefore, what is needed is to provide techniques for network control that exhibit lower amount of downlink transmission, without affecting the required listening of endpoints.
Low throughput networks may not be controlled in the same manner as cellular or even WiFi networks may be fine controlled. This is due to several limitations, which are specific to the fact that, in these networks, endpoints power has to be saved as much as possible and data rates are correspondingly low. The number of packets sent by endpoints is typically very limited, possibly down to one packet a day. This makes statistics based adaptation mechanisms impractical, so WiFi based techniques cannot be used and more explicit data rate control is needed. Another possible limitation is the fact that the size of a packet is usually very small, around 20 bytes, or less. If normal data packets of similar size are used for control, they will contribute to most of the bandwidth use. One other possible limitation is that the listening time of endpoints is limited for power saving, the endpoint spending most of the time in an unreceptive low-power state. This is another reason why normal packets, broadcast/multicast packets may not be used for control. Further, in some deployments that use unlicensed bands, the transmit duty cycle is limited. This is not an issue for endpoints, but impacts greatly the time left for control at network base station level.
Despite these limitations, there is still a need for network adaptation. Link rate adaptation, by varying the data rate of the endpoint, reduces to the minimum the time on air for a given data to transmit: this increases network capacity, and more importantly saves battery life. Transmitted power adaptation comes in addition to link rate adaptation, or can be used alone. This power adaptation also saves endpoint power and increases capacity. It reduces potential interferences to other endpoints transmissions that base stations attempt to receive. Endpoints can be slightly mobile, the environment can change over time, or the network can change over time: this motivates the use of adaptation mechanisms. The adaptation mechanisms have to be as simple as possible to meet the constraints of low throughput networks.
Therefore, it is an aim of the present invention to propose means and methods capable of providing suitable control mechanisms, especially in low throughput networks.